(UNDATED) - Right around the 4th of July holiday is one of the most popular times for vacations when many families pack up and head to places around bodies of water and where it's especially hot.

Anyone can fall victim to a heat-related illness, especially those who aren't used to extreme temperatures.

Dr. Don Bucklin with US Healthworks says, normally, your body cools itself off by sweating - but during hot weather, particularly with high humidity, sweating sometimes isn't enough. He says hydration is the key.

"You have to be ahead on hydration," he added. "You can't wait until you're really really thirsty, or feel sick and then hydrate, because you've already waited too long."

When heat illness hits, he says cramps are usually the first sign followed by intense sweating, nausea and headache. Heat stroke, also known as sun stroke, is the most dangerous and happens when a person's internal body temperature starts to rise. Bucklin says that should be considered a medical emergency because it can be fatal.

Bucklin says some people are more susceptible to heat illnesses than others, including those working outdoors, folks who are very young or elderly and those who are obese. Concerns also increase for chronic alcoholics and people taking some medications.

"Certain tranquilizers, certain anti-hypertensives make you more susceptible to it because they change the fluid balance in your body," Bucklin says. "The other things is, if you are older, your fluid system is less tolerant of big swings."

People who have a heat stroke have body temperatures that reach 104 degrees and higher. Bucklin says in those cases an emergency room visit is mandatory.